1. Field of the Invention
The present invention relates to a linear motor that is available to be used in various industrial devices. Particularly, the present invention relates to a toroidal-coil linear stepping motor and a toroidal-coil linear reciprocating motor that have toroidal coils in their armatures. Further, the present invention relates to a cylinder compressor and a cylinder pump using such a linear stepping motor or a linear reciprocating motor.
2. Prior Art
Japanese unexamined patent publication Hei 10-191619 discloses a conventional linear stepping motor. FIG. 4 of the publication discloses a construction where a movable body 4 having wheels 3 slides on a linear rail 1 on which many stator teeth 2 are formed. Each of cores 8a and 8b of the movable body 4 is provided with small teeth 9 that face the stator teeth 2. When an electric current is applied to coils 28 and 28 that are wound around the respective cores in a predetermined sequence, the movable body 4 moves along the linear rail 1 by electromagnetic force that acts between the stator teeth 2 and the small teeth 9.
However, in the linear stepping motor disclosed in the above publication, since the movable body (a moving element) 4 faces the linear rail 1 as the stator from one side, electromagnetic force so-called “side pull” in a direction vertical to the moving direction (electromagnetic force to bring the movable body close to the rail) acts in addition to the electromagnetic force in the moving direction.
Accordingly, the one-side-facing type linear stepping motor disclosed in the publication requires a guide mechanism such as the wheel 3 for the movable body 4 and a mechanism such as a linear bearing to receive the side pull so that the side pull dose not prevents the linear movement of the movable body, which increases the cost because of a complex mechanism.
On the other hand, as shown FIG. 28, a toroidal-coil two-phase linear stepping motor that consists of a cylindrical stator 1 and a movable rod 2 arranged in the stator 1 has been known. The stator 1 has two sets of stator units 3 and 4 that are arranged in the axial direction and a permanent magnet 5 embedded therebetween. The stator units 3 and 4 are provided with toroidal coils 3a and 4a, and armature yokes 3b and 4b that hold the toroidal coils. On the inner surface of each stator unit, toroidal magnetic teeth 3c and 4c are formed by alternately repeating projections and depressions in the axial direction. The movable rod 2 has many toroidal magnetic teeth 2a that can face the toroidal magnetic teeth 3c and 4c. 
According to the construction of FIG. 28, when the electric current is applied to the toroidal coils 3a and 4a by turns, the movable rod 2 can linearly move. Since the movable rod 2 faces the stator 1 in 360 degrees, the side pull is not generated. However, in the toroidal coil linear stepping motor shown in FIG. 28, the magnetic flux density through the magnetic teeth at the side of the permanent magnet 5 is higher than that at the opposite side thereof, which causes nonuniform distribution of magnetic flux. For example, when the toroidal coil 4a at the right side is excited, the magnetic flux density through the magnetic teeth at the left side of the coil is higher than that through the magnetic teeth at the right side of the coil. On the other hand, when the toroidal coil 3a at the left side is excited, the magnetic flux density through the magnetic teeth at the right side of the coil becomes higher than that through the magnetic teeth at the left side of the coil. This breaks the balance between thrusts of the respective phases, which lowers the positioning accuracy.
Incidentally, the structure shown in FIG. 29 has been known as a compressor for a car's air conditioner. The compressor shown in FIG. 29 reciprocates pistons by driving power transmitted from a car's engine through an electromagnetic clutch. The electromagnetic clutch is provided with a driving wheel 10 that is rotated by the driving power of the engine and a driven wheel 12 that is pressed against the driving wheel 10 to transmit the driving power when the coil 11 is excited. The rotation of the driven wheel 12 rotates a circular plate 13 that is diagonally fixed to the rotation axis of the driven wheel 12. A circular groove is formed on the circular plate 13 to which balls 14 are engaged. Pistons 16 that reciprocate in cylinders 15 are connected to the balls 14, respectively. Rotating the circular plate 13, the balls 14 follow the displacement of the engaged positions on the circular plate 13, which reciprocates the pistons 16 within the cylinders 15. The cylinders 15 have intake ducts and exhaust ducts, and compressed gas is supplied to an evaporator (not shown).
In the mechanism of FIG. 29, a compression ratio can be adjusted by setting the inclination angle of the circular plate 13. However, the inclination angle is determined at a manufacturing stage for each product and it cannot be changed during use. Further, a complicated wobble action applies large mechanical stress on the mechanism, which shortens useful life of the mechanism.
If a linear motor is used as a driving source of a compressor to reciprocate a piston within a cylinder, the compression ratio can be easily adjusted during use and the mechanical stress can be lowered. However, if a piston of a compressor is only connected to a linear stepping motor, respective spaces for the cylinder and the linear stepping motor are necessary, and a mechanism for guiding a movable portion is required inside the linear stepping motor, which hinders from making the device compact.